The European Patent No. EP 1 422 436 discloses a balance spring formed in silicon and covered with silicon dioxide so as to make the thermal coefficient substantially zero around the COSC procedure temperatures, i.e. between +8 and +38° C. Likewise, the document WO 2008-043727 discloses a MEMS resonator which has similar qualities of low variation of its Young's modulus within the same temperature range.
However, the variation of the frequency of the disclosures above can require complex corrections according to the applications. For example, for electronic quartz watches to be able to be COSC certified, an electronic correction based on a measure of the temperature must be effected.